Field
Exemplary embodiments of the invention relate to a light emitting device, and, more particularly, to a light emitting device including a bonding pad soldered to a mounting substrate and having a particular structure capable of minimizing occurrence of voids during soldering.
Discussion of the Background
A high output light emitting device can be obtained by taking into account various design factors such as improvement in luminous efficacy, reduction in package size, and/or reduction in thermal resistance. A flip-chip type light emitting device is one type of the high output light emitting device having such features that is widely used in the art.
Flip-chip bonding means a chip bonding method that utilizes solder bumps to reduce bonding inductance to 1/10 or less. Since substantially no bonding length may exist in the flip-chip bonding, as compared to a conventional wire bonding, such chip packages may be integrated to a higher degree.
To achieve the foregoing design objectives, a flip-chip type light emitting device may be configured to emit light through a substrate in order to reduce light loss in electrode pads. The flip-chip type light emitting device may also include a reflective layer on a p-type semiconductor layer in order to improve extraction efficiency by changing a course of photons traveling towards a mounting substrate into an opposite direction. Further, the flip-chip type light emitting device may have an improved current spreading efficiency, which enables application of low forward voltage.
In addition, although a high output light emitting device typically generates large amounts of heat upon application of high injection current, distance from an active layer corresponding to a heat generation region to a heat dissipation structure in the light emitting device is short, thereby enabling easy heat dissipation and significant reduction in thermal resistance. Accordingly, most high output light emitting devices such as large light emitting devices are of the flip-chip type design.
Various structures have been used for assisting current spreading in a large light emitting device that may utilize a flip-chip bonding. For example, an active layer interposed between a first conductive type semiconductor layer and a second conductive type semiconductor layer may be divided into two or more sections, such that the two or more active layers share one first conductive semiconductor layer.
In flip-chip bonding, a solder bump is melted by application of a heat thereto to realize electrical connection between a bonding pad of a chip and a mounting substrate, and a process of melting the solder bump may be referred to as a reflow process.
In the reflow process, a flux is evaporated and may generate bubbles, which in turn are trapped into the molten solder that generates voids during solidification of the molten solder. Voids act as a main factor that weakens heat dissipation and causes a connection failure between the bonding pad of the chip and the mounting substrate, thereby deteriorating reliability of a light emitting device.
Therefore, there is a need in the art to minimize the occurrence of voids in order to improve reliability of light emitting devices, particularly high output light emitting devices such as flip-chip types light emitting devices.
The above information disclosed in this Background section is only for enhancement of understanding of the context of the inventive concept, and, therefore, may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.